Rammsteiner

if you do not know poeple at xbitlabs and how they work you have no rights to judge their credibility. Secondly TDP numbers don't come from nowhere cos motherboard and heatsinks vendors must know these numbers to design their products and Intel must know these numbers to design packaging. As for the Intel's methods some details can be found in the tech docs:

This specification is the Thermal Design Power and is the estimated maximum possible
expected power generated in a component by a realistic application. It is based on
extrapolations in both hardware and software technology over the life of the component. It
does not represent the expected power generated by a power virus. Studies by Intel
indicate that no application will cause thermally significant power dissipation exceeding
this specification, although it is possible to concoct higher power synthetic workloads that
write but never read. Under realistic read/write conditions, this higher power workload can
only be transient and is accounted in the AC (max) specification.
I'm sure AMD will provide more in depth details on their methodology upon business request.
It's just the way AMD works.